Copenhagen is the greenest city in the world, and its carefully planned green rooftops are helping it reach that spot. The rooftop oases help trap carbon and water, support biodiversity and help the city prepare for the warmer future that's coming thanks to climate change.

The history of Washington features plenty of mudslinging, fighting and division, and that's without even going inside Congress. Here's how the capital developed from the small, dirty, disorganized town it was in the 19th century into today's capital — and how that history still shapes the city.

The history of Washington features plenty of mudslinging, fighting and division, and that's without even going inside Congress. Here's how the capital developed from the small, dirty, disorganized town it was in the 19th century into today's capital — and how that history still shapes the city.

Copenhagen is the greenest city in the world, and its carefully planned green rooftops are helping it reach that spot. The rooftop oases help trap carbon and water, support biodiversity and help the city prepare for the warmer future that's coming thanks to climate change.

Copenhagen is the greenest city in the world, and its carefully planned green rooftops are helping it reach that spot. The rooftop oases help trap carbon and water, support biodiversity and help the city prepare for the warmer future that's coming thanks to climate change.

The history of Washington features plenty of mudslinging, fighting and division, and that's without even going inside Congress. Here's how the capital developed from the small, dirty, disorganized town it was in the 19th century into today's capital — and how that history still shapes the city.